This invention relates to a process for preparing interpolymers of ethylene and at least two or more heteroatom substituted olefin monomers. The process is a high pressure, free radical initiator, polymerization process. The invention also relates to novel ethylene interpolymers having Tm values of at least 50xc2x0 C.
Plastics and elastomers derived from olefins are used in numerous diverse applications, from trash bags to fibers for clothing. Olefin polymers are used, for instance, in injection or compression molding applications, such as extruded films of sheeting, as extrusion coatings on paper, such as photographic paper and thermal and digital recording paper, and the like. Constant improvements in catalysts have made it possible to better control polymerization processes, and thus influence the properties of the bulk material. Increasingly, efforts are being made to tune the physical properties of plastics for lightness, strength, resistance to corrosion, permeability, optical properties, and the like, for particular uses. In addition to chain length and branching, the incorporation of monomers containing functional groups, such as ethers and esters, offers an opportunity to further modify and control the properties of the bulk material. For example, the early transition metal catalyst systems (i.e., Group IV) tend to be intolerant to such functional groups, which often causes catalyst deactivation.
Conventional low density polyethylenes are readily prepared in high temperature, high pressure polymerizations using peroxide initiators. These high pressure free radical systems can also be used to prepare ethylene copolymers containing functional vinyl monomers, but it is important to note that only a small number of monomers can be polymerized in this high energy (e.g., 200xc2x0 C., 30K psi) process, i.e., vinyl acetate and methyl acrylate.
Certain transition metal catalysts, such as those based on titanium compounds (e.g., TiCl3 or TiCl4) in combination with organoaluminum cocatalysts, are used to make high density polyethylene and linear low density polyethylenes (HDPE and LLDPE, respectively), as well as poly-xcex1-olefins such as polypropylene. These so-called xe2x80x9cZiegler-Nattaxe2x80x9d catalysts are quite sensitive to oxygen, sulfur and Bronsted acids, and thus generally cannot be used to make olefin copolymers with functional vinyl monomers having oxygen, sulfur, or Bronsted acids as functional groups.
Zielger-Natta and metallocene catalyst systems, however, have the drawback that they cannot generally be used in olefin polymerization reactions with functionalized monomers. It is known in the art that homogeneous single site transition metal catalysts generally allow for specific control of catalyst activity through variation of the electronic and steric nature of the ligand. Homogeneous catalysts are known to offer several advantages over heterogeneous catalysts, such as decreased mass transport limitations, improved heat removal, and narrower molecular weight distributions.
None of the references described above disclose the copolymerization of olefins with 3,4-epoxy-1-butene (hereinafter xe2x80x9cepoxybutenexe2x80x9d), epoxybutene derivatives, and analogs thereof. Epoxybutene is a readily available compound containing two reactive groups: a double bond and an epoxide. By reaction at one or both groups, epoxybutene can easily be converted into a host of additional compounds.
The preparation of epoxybutene and derivatives thereof, and examples of the same, have previously been described in numerous references, including, but not limited to, U.S. Pat. Nos. 4,897,498; 5,082,956; 5,250,743; 5,315,019; 5,406,007; 5,466,832; 5,536,851; and 5,591,874 which are incorporated herein by reference. Reaction at one or both of these sites affords a host of olefinic derivatives, many of which contain versatile functional groups. Polymerization of epoxybutene has been performed using traditional thermal and free radical initiated reactions, however the pendant epoxide group often does not survive the reaction conditions.
Advances in the polymerization of epoxybutene and its derivatives include the following:
L. Schmerling et al., U.S. Pat. No. 2,570,601 describes the thermal homopolymerization of epoxybutene and the thermal copolymerization of epoxybutene and various vinyl monomers, such as vinyl chloride, vinyl acetate, acrylonitrile, butadiene and styrene.
Polymerization reactions of epoxybutene, in which the epoxide ring is opened to afford polyethers, are known, such as those described in: S. N. Falling et al., U.S. Pat. No. 5,608,034 (1997); J. C. Matayabas, Jr., S. N. Falling, U.S. Pat. No. 5,536,882 (1996); J. C. Matayabas, Jr. et al., U.S. Pat. No. 5,502,137 (1996); J. C. Matayabas, Jr., U.S. Pat. No. 5,434,314 (1995); J. C. Matayabas, Jr., U.S. Pat. No. 5,466,759 (1995); and J. C. Matayabas, Jr., U.S. Pat. No. 5,393,867 (1995).
W. E. Bissinger et al., J. Am. Chem. Soc., 1947, 69, 2955 describes the benzoyl peroxide initiated free radical polymerization of vinyl ethylene carbonate, a derivative of epoxybutene.
Cationic polymerization of vinyl ethers (such as 2,3-dihydrofuran) is known using Lewis acids or proton-containing acids as initiators. These monomers have been shown to polymerize violently through a cationic polymerization mechanismxe2x80x94often at rates orders of magnitude faster than anionic, or free radical polymerizationsxe2x80x94in the presence of both Bronsted and Lewis acids (P. Rempp and E. W. Merrill, xe2x80x9cPolymer Synthesis,xe2x80x9d Huthig and Wepf, 2nd ed, Basel (1991), pp. 144-152). Olefin addition polymerization of vinyl ethers via a transition metal mediated insertion mechanism has not been demonstrated.
In addition, the synthesis of alternating copolymers and terpolymers of olefins and carbon monoxide is of high technical and commercial interest. New polymer compositions, as well as new processes to make polymers derived from olefins and carbon monoxide, are constantly being sought. Perfectly alternating copolymers of xcex1-olefins and carbon monoxide can be produced using bidentate phosphine ligated Pd(II) catalyst systems (Drent et al., J. Organomet. Chem., 1991, 417, 235). These semi-crystalline copolymers are used in a wide variety of applications including fiber and molded part applications. These materials are high performance polymers having high barrier and strength, as well as good thermal and chemical stability.
Alternating copolymerization of olefins and CO using Pd(II) catalysts has been demonstrated by Sen et al., J. Am. Chem. Soc., 1982, 104, 3520; and Organometallics, 1984, 3, 866, which described the use of monodentate phosphines in combination with Pd(NCMe)4 (BF4)2 for the in situ generation of active catalysts for olefin/CO copolymerization. However, these catalyst systems suffer from poor activities and produce low molecular weight polymers. Subsequent to Sen""s early work, Drent and coworkers at Shell described the highly efficient alternating copolymerization of olefins and carbon monoxide using bisphosphine chelated Pd(II) catalysts. Representative patents and publications include: U.S. Pat. No. 4,904,744 (1990); J. Organomet. Chem., 1991, 417, 235; and U.S. Pat. No. 4,970,294 (1990).
Recent advances in olefin/CO copolymerization catalysis include the following:
Brookhart et al., J. Am. Chem. Soc., 1992, 114, 5894, described the alternating copolymerization of olefins and carbon monoxide with Pd(II) cations ligated with 2,2-bipyridine and 1,10-phenanthroline;
Brookhart et al., J. Am. Chem. Soc., 1994, 116, 3641, described the preparation of a highly isotactic styrene/CO alternating copolymer using C2-symmetric Pd(II) bisoxazoline catalysts;
Nozaki et al, J. Am. Chem. Soc., 1995, 117, 9911, described the enantioselective alternating copolymerization of propylene and carbon monoxide using a chiral phosphine-phosphite Pd(II) complex.
None of these references teach the copolymerization of olefins with carbon monoxide and functionalized olefins, like epoxybutene and related compounds.
U.S. Pat. No. 6,090,900 discloses homopolymers of olefin monomers having polar functional groups, and copolymers of these monomers with each other and with non-polar olefins, and optionally carbon monoxide.
The present invention is directed to interpolymers comprising ethylene and at least two, or more, monomer units selected from heteroatom substituted olefin monomer units derived from a compound of the formula XV. 
wherein E and G represent the same or different heteroatoms selected from oxygen, nitrogen, and sulfur, which are bound to a hydrogen atom, a hydrocarbyl group, or a substituted hydrocarbyl group, or are joined by a linking group; and n is 0 or an integer from 1-20; or 2,3-dihydrofuran, or vinylcylcopropane. The novel products of the present invention are the interpolymers as desrcribed herein that are characterized by having a melting peak temperature (Tm), as determined by the procedure specified herein, of equal to or greater than 50xc2x0 C., preferably from equal to or greater than 50xc2x0 C. to about 115xc2x0 C.
The novel process for preparing the interpolymers comprising ethylene and the at least two or more monomer units selected from the specified heteroatom substituted olefin monomer units or 2,3-dihydrofuran, or vinylcyclopropane, including the novel interpolymers of the present invention characterized by having a melting peak temperature (Tm) of equal to or greater than 50xc2x0 C., preferably from equal to or greater than 50xc2x0 C. to about 115xc2x0 C., is comprised as follows. The interpolymers are produced by polymerization of the monomers in any suitable high pressure reactor known for the polymerization of ethylene-containing monomer mixtures, examples of which include autoclaves, tubular reactors and the like. In general, the interpolymerization of the monomers is conducted at a temperature of from about 150xc2x0 C. to about 350xc2x0 C., at a pressure of from about 68 to about 304 MPa""s (about 671 to about 3000 atmospheres), and for a period of time of from about 2 to about 600 seconds. The interpolymerization process is conducted in the presence of at least one, or more, free radical initiators, that are defined as chemical substances that, under the polymerization conditions utilized, initiate chemical reactions by producing free radicals.